122 MASS. KXI'KKIMKXT STATION BULLKTIX 276 



desired lowering of \)ll value of the soil and the (juanlity wliieh may he aj)- 

 plied with safety to jilants, may Aary with the soil and cannot he predicted 

 with any degree of exactness except hy preliminar\- experiments with the 

 particular soil. 



In one series of these preliminary experiments, the same acid treatments 

 were ajijilied to two soils. One of these, a water-deposited fine silt loam high 

 in organic niattei, ivas well butfered and resisted change in its pH value. The 

 other soil, an ice-deposited stony loam, was not as well buffered and its pH 

 value was consequently more readily lowered by the same application of an 

 acid. As has been pointed out by others (28, 21) the effect of an application 

 of acid on the pH value of soil and on plants and fungi in that soil depends 

 on the type of soil. Acids in the the same quantities were somewliat more 

 toxic to plants in the well-buffered soil. 



FIELD EXPERIMENTS 

 Methods and Plan of Work 



Tliese experiments (except as otherwise indicated) were carried on in a 

 field the history and plot treatments of which up to 192.5 have already been 

 described (.5). Certain plots had received applications of lime to a total of 

 5 tons per acre, the last of which was applied in 1923. In these limed plots 

 pH values were high enough to favor Thielavia basicola, black root-rot was 

 severe, and yields of tobacco were consequently low. Tobacco was grown on 

 all plots from 1922 to 192.5 inclusive. Soil treatments and crojis of each plot 

 from 1926 to 1929 inclusive were as recorded in Table 9. 



The fertilizers used each year and the amounts of each material are shown 

 in Table 10. These were applied immediately before tobacco plants were set. 



In 1926 sulfur (inoculated), 200 or 400 pounds per acre, or sulfuric acid, 

 1800 pounds, together with orthophosphoric acid (80 per cent), 440 pounds 

 per acre, were ai>plied to the plots so indicated in Table 9. This was done 

 one month before plants were set. The acids and the sulfur were harrowed 

 into the soil immediately after their application. In 1927 sulfur and the acids 

 were applied again and in the same amounts to the plots named in Table 9, 

 two months before the tobacco plants were set. Some plots received these 

 treatments, therefore, in one year only, and others received them in two suc- 

 cessive years. No acidifying chemicals were applied after 1927. 



In order to determine how tobacco compared with some other crops in 

 removing lime from the soil and in lowering the pH value of soil, timothy 

 was planted in the fall of 192.5 and alfalfa and alsike clover in the spring of 

 1926 on the ))lots indicated in Table 9. The hay crops were grown on these 

 ))lots in 1926 and 1927. In 1928 half of each hay plot was again set with 

 tobacco, and in 1929 and 1930 the other half of each hay plot was again used 

 for tobacco. There were thus available for com])arison jilots on which tobacco 

 was grown every year and plots on which tobacco was grown following two 

 or three years of each of these other crop.s — alfalfa, alsike clover, or timothy. 

 I'^ach year the tobacco from each of the several plots was cut, cured, 

 stri])ped, and .sorted separately. The fire-holding capacity or duration of burn 

 of samples of leaf from each plot was determined in strip tests.' The quanti- 

 ties of calcium and magnesium oxides removed in each crop (including stalks 



'The burn of the leaves was initiated by means of an electrical resistance coil. 

 Five leaves from each grade were used and four tests were made on each loaf. 



